Internal combustion engines create noise which is generated by the sudden expansion of internal combustion engine chamber exhaust gasses. As the combustion gasses are exhausted from each cylinder of the engine, a sound wave front travels at rapid sonic velocities through the exhaust system. Efforts have continued over many years to reduce or muffle the noise caused by combustion gasses.
U.S. Pat. No. 5,952,625 granted on Sep. 14, 1999 to Ronald G. Huff describes two major muffler classifications, namely, dissipative and reactive mufflers. Dissipative mufflers are typically composed of ducts or chambers filled with acoustic materials, such as fiberglass, steel wool or porous ceramics. Such materials absorb acoustic energy and transform it into thermal energy. Reactive mufflers are composed of a number of interconnected chambers of various sizes and shapes in which sound waves are reflected to dampen or attenuate waves of a set frequency, typically resonance frequency. Each type of muffler has its disadvantages and the patent seeks to improve reaction mufflers of the side branch type through the utilization of a plurality of concentric sound passages through which exhaust gasses flow from an inlet to an outlet of the muffler along back-and-forth exhaust gas passages. The muffler also includes a central cylindrical passage between the muffler inlet and outlet and the latter is surrounded by the back-and-forth exhaust gas passages which are selectively provided with closed ends (sound reversal walls) for effecting sound dampening or attenuation at selected frequencies.
U.S. Pat. No. 6,089,347 granted on Jul. 18, 2000 to Ray T. Flugger discloses a muffler in which sound is reduced by incorporating a plurality of axially spaced cone-shaped partitions within a chamber of the muffler. Outward ends of the partitions defined between them spaces which are oriented with respect to the flow path of exhaust gasses so as to create a low pressure region within the spaces creating something of a venturi effect wherein exhaust gasses exteriorly of the partitions create low pressure regions between the partition walls. The orientation of the spaces between the partition walls with respect to the exhaust flow path exteriorly thereof is such that sound vibrations which enter the spaces and reflect off the partitions and the walls thereof as sound vibrations are attenuated between the partitions prior to exiting the muffler.
U.S. Pat. Nos. 5,530,214 and 6,105,716 issued respectively on Jun. 25, 1996 and Aug. 22, 2000, each in the name of Clyde A. Moorehead et al., disclose respectively a VENTURI MUFFLER and VENTURI MUFFLER HAVING PLURAL NOZZLES. In each case the venturi throat is sized to increase the speed of the gas flowing therethrough to decrease or attenuate noise.
U.S. Pat. No. 5,892,186 granted on Apr. 6, 1999 to Ray T. Flugger discloses a muffler for internal combustion engines which includes a central dispersion shell which tapers from an inlet to a minimum diameter at a restriction which is effective in attenuating noise by substantially reducing straight-through transmission of sound and by causing noise components to converge together thereby achieving sound frequency cancellation. A dispersion shell diverges from the restriction to an outlet and is surrounded by a perforated right-cylindrical shell which in turn is surrounded by a thermally insulating fiberglass layer and a ceramic fiber blanket.
U.S. Pat. Nos. 7,243,757 and 7,331,442 granted respectively on Jul. 17, 2007 and Feb. 19, 2008 to Karl Bernard Stuber and Alan Wall, respectively, are further examples of mufflers having inner passages provided with a variety of partitions, vanes, baffles or the like to reflect internal combustion exhaust gasses as they travel from inlet to outlet to reduce or attenuate exhaust noise.